Portable grinding machine



FIG. 1 is a perspective view of a portable grinding machine showing our new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a rear view thereof; and

FIG. 7 is a bottom view thereof. 

The ornamental design for a portable grinding machine, as shown. 